Natalie Portman has credited her friendship with Ashton Kutcher for making sex scenes fun.

In Ivan Reitman's film No Strings Attached the actress' character Emma soon falls into bed with her former childhood friend Adam (Ashton), and Natalie reckoned their closeness made her feel less uncomfortable.

"We obviously had to do stuff that could be really awkward, and when you just know that the person there won't overstep boundaries, you can just play and be silly together," Natalie told Entertainment Tonight.

"The whole point of any of the sex scenes is to make you laugh, so at least we had that, that we could be really ridiculous in those scenes."

Ashton admitted the scenes were more technical than sexy.

"At a certain point you just let it flow. It becomes really technical," he said.

He added: "The towel is your best friend, man. You can't go wrong with a good towel. I was sort of requesting a bigger towel [for one particular scene], but they left me with a hand towel."